It always makes me happy to know that gardeners understand the value that most basic of tasks — testing the soil — provides them in improving their gardening success. I do realize though that taking a soil test is not the most glamorous of tasks, and it’s true that our lab has raised their costs over the last few years. So, while it does cost you money, it can also save you money to know your soil’s nutrient needs and whether there are any issues that should be managed.
Over the last few years, two issues are showing up more often in local soil tests, and it’s happened twice just recently. These include high nutrient levels of phosphorus and potassium and high salinity levels. Nitrogen (N), being water-soluble, should be added each year, but phosphorus (P) and potassium (K) aren’t used by plants as much. High levels of P and K are really not a good thing since they can lead to plant growth problems, so it’s rarely necessary to apply a complete fertilizer, meaning those containing N, P, and K, year after year. And if you don’t have to do it you can save money.
The other issue involves increased salinity levels. Since this is a semi-arid region, it’s pretty common to have soils with higher salt levels than those areas receiving more rainfall. High soil salinity levels can result in plants being unable to draw in as much water as they need, even when the soil is sufficiently moist. With plants such as vegetables, high salinity in soil can result in lower yields. High salinity levels can also kill some plants over time, although as with most living things there are plants that are more tolerant than others.
We generally haven’t seen naturally high salinity levels here in Grand County, other than in a few areas of the county. A salt is an inorganic mineral that dissolves in water. There can be many types, including sodium, calcium, potassium, magnesium, chlorides, sulfates and bicarbonates. While many of these are found naturally in our soils, the nutrients found in fertilizers also are salts, so adding excessive amounts adds to the salinity. In addition, salts are found in manures and high levels of manure usage can result in high levels of soil salinity. We can also see soil salinity levels rise in soils that are poorly drained, where there is increased evaporation from the soil surface, where the irrigation water used has increased salinity levels, or where irrigation is only done lightly, without enough water to flush salts below the root zone of plants.
So what can you do? For a start, don’t keep adding fertilizers every year that aren’t needed. In this case, more really is not better. If you use manures, be careful with the amount you use since they will add salts to your soil, and some manures such as poultry manure can also add large amounts of potassium and phosphorus over time. Mulching soils, especially in our area, can reduce soil evaporation resulting in less concentration of salts near the soil surfaces. When you do irrigate do so well — ½ to 1 inch of water — rather than just enough to moisten the soil surface.
Lastly, if you do find that you have high salt levels you can leach the salts down below the root zone of the plants since salts are water-soluble. You need good soil drainage so the water percolates down through the soil, and ideally, a good clean source of irrigation water. Applying 6 inches of water over a limited time, say 24 to 36 hours, can reduce salinity levels by 50 percent. It’s important that this is done in a short period of time since you are putting the salt into solution and pushing it down through the soil. Smaller, shorter irrigation times just move the salts within the root zone.
Thought for the day: “How can I stand on the ground every day and not feel its power? How can I live my life stepping on this stuff and not wonder at it?” —William Bryant Logan.
Previous articles are available at The Times-Independent website, www.moabtimes.com. Have an idea you’d like Mike to consider writing about? Want more information about these topics? Call the Utah State University Extension Grand County office at 435-259-7558 or email Mike Johnson at firstname.lastname@example.org.